Oil shales are widely distributed throughout the world and throughout the geologic column. Large amounts of oil may be derived from them and they can be made a substitute for naturally occurring liquid petroleums.
"Oil shale" is a term applied to several kinds of organic and bituminous shales consisting of varying mixtures of organic matter with shale and clay. The organic matter is mainly in the form of a mineraloid, called Kerogen.
There are two types of kerogen--a coaly type and an oily type. The oily type of kerogen is the type this invention applies to. Although oil shales are widely distributed throughout the world, there are not many places where they are concentrated in amounts great enough to exploit commercially. The Green River Formation is one such place. This formation covers thousands of square miles and is from 1500 feet to 2000 feet thick.
Great amounts of oily type kerogen are contained in the shales of the Green River Formation, located in Utah, Colorado and Wyoming. There are billions of barrels of oil in solid form (kerogen) located in these shales. The present invention relates to the recovery of the oil from the kerogen containing shale in this formation.
Oil can be recovered from these kerogen shales by heating. This invention puts forth a method of heating the kerogen in situ and drawing off the oil thus formed as from a normal liquid petroleum oil well.
Various solutions for the in situ recovery of the kerogen have been proposed. Common to most efforts is the use of thermal breakdown. The kerogen is heated in situ and breaks down into shale oil and gas which can be efficiently recovered. Generating the required heat for the chemical decomposition (pyrolysis) usually has been accomplished by either burning a portion of the kerogen or by injecting or circulating hot fluids or steam.
Previous solutions have all had significant disadvantages. For example, U.S. Pat. No. 4,408,665 to Dougan requires that the shale be water-flooded and is a supplement to mining when the mine gets flooded. Recovery is dependent on the use of the water to float-out the shale oil. Kerogen located in shale not water-flooded and therefore cannot use this recovery process. Another disadvantage commonly encountered is the requirement that some fuel be burned during the process of recovery. With these prior art methods, either fuel must be burned on the surface to heat the fluid to be injected into the shale or some of the kerogen must be burned to generate the heat in situ. Additionally, the burning of fuel during the recover process creates unnecessary pollution and makes automation of the recovery process extremely difficult.
A solution is needed that is capable of generating enough heat and pressure such that the process will work in impermeable shale and does not require the burning of fuel, is pollution free, can be completely automated therefore requiring little or no maintenance and is not labor intensive.